Silicon photonics chips require electric current and light to be applied in order to function. The electric current is provided in a similar fashion to that used with other types of silicon chips. However, various approaches have been used, thus far, to provide the light input to PIC substrates to form a PIC. The main approach used for optical coupling is based on active alignment. Using active alignment, light may be generated by powering a laser, energy from which is typically detected downstream. To peak optical coupling, the laser, fiber, lens, or other intermediate objects are precisely moved relative to the detector before fixing the geometry. This approach requires electrical contact to the laser early in the assembly process, which can complicate manufacturability. Below are three examples of light coupling to PIC substrates.
A first example uses an optical fiber that brings light to a PIC substrate. This example uses active alignment of the optical fiber to the PIC substrate, which can be time-consuming and expensive and can produce fragile assembly. Using optical fiber also consumes a large amount of space not just for the fiber, but also for a packaged semiconductor laser that may be connected to the other end of the optical fiber.
A second example uses an externally packaged semiconductor laser diode with a lens and other optical elements, as disclosed in U.S. Pat. No. 8,168,939. Although this example reduces an amount of space used compared to the first example, it still consumes too much space, as well as adds costs associated with the optical elements and required assembly and packaging. This example also typically requires activation of the laser during alignment.
A third example uses a cleaved or etched facet semiconductor laser directly with a silicon photonics chip. This example minimizes overall size, however, it requires either active or passive alignment of the semiconductor laser to the silicon photonics chip, which are time-consuming and add cost.
To address the above shortcomings, some effort has been placed on using passive alignment to reduce cost and speed assembly. In passive alignment, optical fiducials on parts are typically viewed with a microscope imaging system, and the parts are then simply mated and fixed without measuring the optical coupling performance. Passive alignment can be simple and quick, but is severely limited by the cost and time required to achieve needed precision. Resulting alignment precision below 15 microns is prohibitively expensive.
The above challenges and shortcomings associated with current delivery of light to PIC substrates have hindered the ability to use PICs in a beneficial way in applications such as data center connectivity.